I'll preface this by saying I know little to nothing about tuning these cars and may have a few misconceptions about how things work, please feel free to correct me.
This car has been on the same 22psi tune for 4 years, with 0 issues until now.

Few weeks ago while stuck in traffic the engine light came on, along with the Service Brake message on the dash, no brake warning light or ABS light, it threw two codes, C1100 and P2237, brake booster solenoid and front o2 sensor respectively. At this same time my lambda started jumping all over the place, where it usually stayed within a few hundredths off of 1.00 before.

Cleared the codes and continued driving, the erratic lambda persisted and a few days late the P2237 came back, but no C1100.

Replace the front o2 with an NGK sensor, I know it's best practice to replace with Delco but couldn't get one, NGK lists as a direct replacement and is a heated wideband sensor.

After the o2 replacement the code never returned, but the erratic lambda has continued.

Now I see the commanded lambda/afr is fluctuating as well, my understanding is that during closed loop operation commanded lambda/afr should be 1.00/14.7 all the time, with the exception being during DFCO, is that correct?

If that is my correct understanding, what could cause these values to suddenly start fluctuating?

I can't log with HPT right now as my laptop had an accident and is no longer with us, so I'm just going off the Interceptors, which seem to be reading accurately.

Made a cell video to try and show what's happening, not sure if it's helpful or not.

 

I know you don't have your laptop right now, but if on the off chance you can borrow one or you do get one..you can hook up VCM Scanner and go to "Special Functions" I think it is called, and go to the tab where you can command a specific AFR, and lock it in so it's commanding exactly 14.7, then check your gauge to make sure it is matching or not..🤷‍♂️

 

I'm 98% certain that does not work on the LNF. It's a strange ECU and a lot of the nice features are not available.

 

You what I'm pretty sure you are right..

I got my 08 and HPTuners and all excited to toy with it, plugged it in, and saw you can't log a lot of stuff. I had assumed it was because I have a Trifecta switchable tune..but I guess they're all like that?

 

From a logging standpoint you have to select the proper channels, most of the default channels or generic channels are a no go for it. You don't have any live control options like the LS engines do, where you can modify timing or cam position live (like on a dyno to see the change instantly)

 

Same for the LSJ... can't make spark adjustments live... so dialing in a spark table is a royal PITA.

 

Well that sucks. I can't rear or write to the trifecta pcm which sucks big time. Looks like I will need to score another pcm and license the original VIN and the donor vehicles VIN, idk.

At least like that I can always swap the old PCM in and have the switchable trifecta tune if ever need be.

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As far as the original post though,

So the commanded AFR is shooting up to just under 30, which is 2.00 lambda roughly...?

And you're at steady throttle position? Not letting off the pedal at all?

It is an electronically controlled throttle body..can you bring up the actual throttle position vs the etc position commanded? Maybe the pcm is moving the throttle blade and you are hitting DFCO?

 

The commanded AFR maxes out during fuel cutoff, once I get back on the throttle slightly to maintain speed that's when the commanded afr drops below 14.7.

 

On the LNF after it warms up its closed loop full time. The wideband sensor provides feedback for fueling adjustments so it doesn't change to what normally is thought of as "open loop" for WOT.

The command lambda dropping when you give it throttle could be connected to your tune and you just never noticed it before the o2 sensor code.

Have you done a boost leak lately? I know it sounds like a broken record, but if you have a leak that can cause strange issues